1. Field of the Invention
The invention generally relates to a rail vehicle and method for the installation and removal of railroad crossties or sleepers. A tie exchanging apparatus extracts and loads old ties, and unloads and installs new ties. The apparatus comprises at least one tie distribution car, a tie collection car and an increased capacity storage car, each having interconnected guide rails bridging between cars, permitting tie loading and transport vehicles to move from car to car. The tie loading and transport vehicles transfer old ties to the storage cars from a location where the old ties are being removed from underneath the rails. At the same time, new ties are transferred from the storage cars to a location where a tie ejection apparatus places them along the rails for installation.
2. Prior Art
Railways comprise a bed of ballast material such as size four stones, in which ties are partly embedded to support rails attached to the ties at a specific gauge width, elevation and the like. The rails rest on tie plates and the rails and tie plates are fastened to the ties by spikes, bolts, clips or similar fasteners. In the United States, most rail ties are made of wood, which helps to absorb shock as trains pass. Concrete ties can also be used. Over time and with traffic, compressive and shearing forces damage the ties and loosen the fasteners. Ties also deteriorate due to weather. As a result, it is necessary to replace the ties as a matter of regular track maintenance.
Typically, ties are selected for replacement and preliminarily marked. The selected ties are disengaged from the rails by removing their fasteners, for example by pulling their spikes, and are pulled laterally from under the rails. A new tie is inserted. Tie plates, spikes and anchors are installed to couple the rail to the tie. The ballast is then rearranged by tamping and vibratory stabilization, often accompanied by realignment and elevational adjustments to the track. A selection of ties can be replaced, or all the ties can be replaced, in which case the tracks are lifted and rethreaded onto the new ties.
Railway ties are usually replaced using a number of special purpose rail cars that service a section of track while traveling over that section. Specialized rail cars may have one or more of spike pullers, tie extractors and inserters, tampers, stabilizers, etc., for serving the successive steps, including transporting new ties to the site and removing the old ties that have been extracted. It is efficient to use the same tie storage cars to bring new ties and to take away worn ties, namely by moving collected old ties to a location in the tie storage car from which new ties were previously unloaded, in a continuous operation. To accomplish this, in addition to having cars with storage space for ties, a track maintenance apparatus can include various transport conveyors, tie removal devices and cranes for manipulating the ties.
An example of a rail based tie exchange system is disclosed in commonly owned PCT Application No. PCT/US97/23156. A tie transfer rail vehicle exchanges old ties for new ties and comprises a plurality of gondola type cars with closed sidewalls and open tops. The tie exchanging operation commences with ties being drawn out from beneath the rails and placed on the rails for pick up by a tie pick-up device which can place the ties on a conveyor leading to an accumulating location. The tie pick-up car alternatively can have a collection cage at the front at track level, to pick up extracted ties left on the rails. A conveyor transports the ties to a temporary collection area from which they can be loaded into a storage car.
The tie exchanging operation commences with the old or existing ties being drawn out from beneath the rails and placed on or alongside the rails for pick up by a tie pick-up device which can place the ties on a conveyor leading to an accumulating location. The old tie pick-up car alternatively can have a collection cage attached to its front at track level to pick up old ties lying on the rails. The old tie pick-up car has a conveyor which transports the tie to a temporary old tie collection area which is located on the old tie collection car.
A plurality of gondola storage cars hold new ties for distribution and collected old ties, space for storage of old ties being made available as new ties are unloaded and distributed. The storage cars can be coupled between a tie distribution car at the rear of the apparatus and the tie collection car at the front. Thus it is necessary for tie transport vehicles to shuttle back and forth between an old tie loading point and an available location for storage of used ties, and between available new ties and a tie distribution point. The positions at which used ties are stored and new ties are available varies as work progresses and the new ties in the gondola cars are gradually replaced with collected used ties. Typically these points move in one direction or the other between the front and rear of a number of successive gondola cars. The storage cars have guide rails along their tops, including telescoping hinged sections which bridge between successive cars, to allow at least one tie transport vehicle to travel along the length of the storage cars.
The transport vehicle or vehicles move the old ties from the temporary tie collection area to a storage car. The transport vehicle also loads and moves new ties from the storage cars to the tie distribution car where they are distributed along the rails for installation.
Although this rail based tie exchange system accomplishes tie removal and distribution in an integrated manner, it fails to efficiently store and distribute new ties along the rails. The gondola cars used for storage have closed sides which prevent or make difficult the storage of ties in a lateral orientation. Elongated ties, having larger than normal dimensions, will not fit between the walls of the storage car. Thus, the ties must be longitudinally oriented within the car which takes more space per tie limiting the amount of ties which can be stored within the car. Once the space for storing ties is exhausted the tie exchange vehicle must cease operation and return to a location where old ties can be unloaded and the supply of new ties replenished.
Tie distribution is accomplished by a ramped conveyor which sporadically and intermittently discards ties along the rails. The conveyor is unable to place ties along the rails in a precise manner. For example, the point at which a tie is discarded often does not correspond to the place where the tie will be inserted under the rails. This requires additional manipulation of the tie before it can be inserted under the rails. Namely, the tie must be picked up and moved to the point along the rails where it is inserted, slowing the tie replacement operation.
Accordingly, it would be advantageous to provide a rail based tie exchange vehicle and a method of exchanging ties which optimizes and increases storage space and efficiently distributes ties along a railway for installation.